Conical disk pair for a belt-driven conical-pulley transmission

ABSTRACT

A sensing device integrated into a conical disk pair has a sensing piston, which is movable relative to the input shaft over a radially stepped guide surface formed on a shaft and a corresponding opposing stepped surface formed on the sensing piston. The steps form a damping chamber between the guide surface and the opposing surface, whose volume changes when the sensing piston moves relative to the shaft.

The invention relates to a conical disk pair for a belt-drivenconical-pulley transmission.

Belt-driven conical-pulley transmissions, also known as CVTtransmissions, such as are employed for example in motor vehicles,contain two pairs of conical disks which are encircled by an endlesstorque-transmitting means, for example a plate link chain. By changingthe spacing between the conical disks of each conical disk pair inopposite directions, the transmission ratio of the transmission can bevaried continuously. Advantageously, a conical disk pair, preferably theone on the power input side, includes an integrated torque sensor withwhich the torque acting from a drive engine is detected and a pressurebetween the conical disks of the corresponding disk pair is changed inaccordance with the torque.

Such an inherently known conical disk pair will be described below onthe basis of FIGS. 1 and 2, which show a longitudinal section through aconical disk pair with sensing pistons located in different positions.

According to FIG. 2, a pair of conical disks of a belt-drivenconical-pulley transmission has an input shaft 10 that is made in onepiece with a fixed disk 12. Situated on shaft 10, axially movable butconnected to the shaft 10 in a rotationally fixed connection, is amovable disk 14. An endless torque transmitting means (not shown)circulates between the conical surfaces of disks 12 and 14 and theconical surfaces of another pair of conical disks (not shown).

On the back side of movable disk 14 in its radially outer area, acylindrical ring 16 with two walls at a radial distance from each otheris rigidly attached, in which a piston 18 operates, so that on the rightside of piston 18 according to FIG. 1 a first pressure chamber 20 isformed which can be subjected to hydraulic pressure through radial holes22 bored in movable disk 14, a ring space 24 between movable disk 14 andshaft 10 and a radial hole 26 and an axial hole 28 bored in shaft 3,which hydraulic pressure is changeable to adjust the transmission ratio.

Piston 18, which is ring-shaped on the whole, is rigidly connected to asupport ring 30 which is cup-shaped on the whole, which for its part isrigidly connected to shaft 10. On the inner side, a ring-shapedcomponent 34 formed with formed surfaces 32, which is rigidly connectedto the shaft 10, rests against the support ring 30.

Also situated inside the support ring 30, axially movable, is a sensingpiston 36 which is ring-shaped on the whole and is sealed against thecircumferential surface of shaft 3 and an inner circumferential surfaceof ring-shaped component 34. Sensing piston 36 is designed with aprojection directed toward movable disk 14, on the back of which shapedsurfaces 38 are formed which constitute opposing surfaces to the shapedsurfaces 32. Situated between shaped surfaces 32 and 38 are rollingelements, in the illustrated example balls 40.

Between sensing piston 36 and movable disk 14 a second pressure chamber42 is formed, which may be subjected to hydraulic pressure through asupply line 44 leading through the shaft 10, the hydraulic fluid beingremovable through a drain line 46 which is also formed in shaft 3.

The effective cross section of the inflow orifice 48 that leads into thesecond pressure chamber is determined by the axial position of movabledisk 14. The free cross section of the drain orifice 50 leading out ofthe second pressure chamber 42 is determined by the position of sensingpiston 36. Sensing piston 36 projects through gaps in the support ring30 with axial arms 52 that are preferably spaced at equal intervals inthe circumferential direction. The radial outer surfaces of the arms 52are provided with axially and radially directed gearing, which is meshedwith inner gearing of an input wheel 54, which is supported and isaxially essentially immovable on an external shell 56 of a bearing whichis designated in its entirety as 58.

The construction and the function of the conical disk pair described sofar are known and will therefore be explained only briefly.

When there is a torque from the rotationally drivable input wheel 54acting on sensing piston 36, this torque is transmitted via the shapedsurfaces 38, the balls 40 and the shaped surfaces 32 to the support ringwall 30 and thus to the shaft 3. The shaped surfaces are designed sothat sensing piston 36 moves to the right according to FIG. 1 as thetorque increases, so that the outflow orifice 50, which is notcompletely covered by the sensing piston in the basic or startingposition of the conical disk pair depicted in FIG. 1, is increasinglyclosed. FIG. 2 shows the arrangement of FIG. 1 with very high torque, atwhich the sensing piston 36 is shifted as far as possible to the rightand completely covers the outflow 50. As the effective size of theoutflow 50 becomes smaller, the pressure in second pressure chamber 42increases, so that a pressure which depends on the input torque acts onmovable disk 14.

Advantageously, to support the free ends of the arms 52, a support ring60 is provided which is in contact with the radially inner sides of theend areas of the arms 52 and forces them outward, so that the outergearing of the arms is forced into secure meshing with the inner gearingof the input wheel 54.

The arms 52 are advantageously formed on a ring piece that is welded tothe sensing piston 36, as shown, from where they project axially. Inthis way the welding of the arms or of the ring piece is relieved ofbending forces acting directly on the arms in a circumferentialdirection.

A peculiarity of conical disk pairs with integrated torque sensor, asdescribed, consists in the fact that torque vibrations can occur throughthe gearing, depending on mass inertias and rigidities in the powertrain of a vehicle, the damping of the overall system and of supportgradients over the transmission ratio. Such torque vibrations causecomfort problems, or possibly even an overloading of the transmission.The problems become more severe as the maximum permissible torque of adrive engine increases.

The object of the invention is to create a remedy for the forenamedproblem.

A solution to this problem is created with a conical disk pair for abelt-driven conical-pulley transmission, which conical disk pairincludes a shaft that is rigidly connected to a fixed disk, a movabledisk that is situated on the shaft so that it is axially movable androtationally fixed, a torque sensing device with a shaped surface thatis rigidly connected to the shaft and another shaped surface that isrigidly connected to a sensing piston that wraps around the shaft and isaxially movable relative to the shaft and rotatable, which sensingpiston is engaged with a rotary-drivable input wheel in a rotationallyfixed and axially movable engagement, and rolling elements situatedbetween the shaped surfaces, the shaped surfaces being designed in sucha way that when there is a change in the torque acting between thesensing piston and the movable disk, the axial position of the sensingpiston changes due to shifting of the rolling elements situated betweenthe shaped surfaces onto the shaped elements, and the sensing pistonincreasingly closes a radial outflow orifice formed in the shaft forfluid to flow out of a pressure chamber bounding on the sensing piston,and where in addition a guide surface formed on the shaft for thesensing piston and a corresponding opposing surface formed on thesensing piston are each formed with a radial step, so that a dampingchamber that contains fluid during operation is formed between the guidesurface and the opposing surface, whose volume changes when the sensingpiston is moved axially relative to the shaft.

According to the invention, the axial movability of the sensing pistonrelative to the input shaft is damped by the fact that hydraulic fluidmust flow into or out of the damping chamber provided according to theinvention. The flow capacity which this requires, which is the cause ofthe damping achieved, can be set appropriately by matching the change involume of the damping chamber that accompanies a predetermined relativemovement of the sensing piston and the cross sections of passages thatconnect the damping chamber with the surroundings, for example acentering gap of the guide of the sensing piston on the input shaft.

Advantageously, a fluid connection occurs between the damping chamberand the surroundings, exclusively between the guide surface and theopposing surface.

In a preferred embodiment of the conical disk pair according to theinvention, a sealing ring is situated between the sensing piston and theshaft on the side of the damping chamber facing away from the outfloworifice.

It can be advantageous if the sensing piston is engaged with the inputwheel on its side facing away from the movable disk.

The invention will be described below on the basis of schematic drawingsin exemplary form and with additional details.

The figures depict the following:

FIG. 1: an enlarged detail of FIG. 2 in the area where the sensingpiston is guided on the input shaft,

FIG. 2: a longitudinal section through a conical disk pair according tothe existing art; and

FIG. 3: a longitudinal section similar to that in FIG. 2, but with thesensing piston in a different position.

As can be seen from FIG. 1, which shows a detail from FIG. 2 modifiedaccording to the invention, input shaft 10 is designed with a guidesurface 60, which has a radial step 62 at a distance from outfloworifice 50. An opposing surface 64 of sensing piston 36 guided on theguide surface 60 is likewise designed with a radial step 66, so that adamping chamber 68 is formed between the steps 62 and 66, whose volumechanges when sensing piston 36 moves axially relative to input shaft 10.On the left side of step 66 between sensing piston 36 and input shaft 10a sealing ring 70 is situated, so that damping chamber 68 is connectedto the outflow orifice 50 or the second pressure chamber 42 only througha passage between opposing surface 64 on the right side of step 62 or 66and guide surface 62 or 66 on the right side of step 50. This passagecan be formed by an annular gap between the guide surface and theopposing surface which is the result of their radial dimensioning andforms a guidance gap, or may be formed specifically by one or more smallchannels.

As it is enlarged, the damping chamber sucks in hydraulic fluid from theoutflow orifice or the second pressure chamber, which flows out whendamping chamber 68 is made smaller. The energy converted in the processas a consequence of the flow resistance, which has the effect of dampingthe axial motion of the sensing piston 36, can be adjusted appropriatelyby dimensioning the change in the volume of damping chamber 68, which isconnected to a movement of sensing piston 36, as well as thedimensioning of the cross section of flow between damping chamber 68 andoutflow orifice 50 or second pressure chamber 42. With increasing stepheight and decreasing cross section of the centering gap between thesensing' piston and the guide surface, for example, the dampingincreases.

REFERENCE NUMERAL LIST

-   10 input shaft-   12 fixed disk-   14 movable disk-   16 cylinder ring-   18 piston-   20 first pressure chamber-   22 bore-   24 ring chamber-   26 radial bore-   28 axial bore-   30 support ring-   32 shaped surface-   34 ring-shaped component-   36 sensing piston-   38 shaped surface-   40 ball-   42 second pressure chamber-   44 supply line-   46 drain line-   48 inflow orifice-   50 outflow orifice-   52 arm-   54 input wheel-   60 guide surface-   62 step-   64 opposing surface-   66 step-   68 damping chamber-   70 sealing ring

1. Conical disk pair for a belt-driven conical-pulley transmission,which conical disk pair includes: a shaft (10) which is rigidlyconnected to a fixed disk (12), a movable disk (14) which is situated onthe shaft so that it is axially movable and rotationally fixed, a torquesensing device having a shaped surface (32) that is rigidly connected tothe shaft and another shaped surface (38) that is rigidly connected to asensing piston (36) that encircles the shaft and is axially movable androtatable relative to the shaft, which sensing piston (36) is engagedwith an input wheel (54) that is rotatably supported on the shaft sothat it is rotationally fixed and axially movable, and roller elementssituated between the shaped surfaces, the shaped surfaces being designedin such a way that when the effective torque between the sensing pistonand the movable disk changes, the axial position of the sensing pistonchanges due to the rolling elements (40) situated between the shapedsurfaces shifting onto the shaped surfaces, and the sensing pistonincreasingly closes a radial outflow orifice (50) formed in the shaftfor fluid to flow out of a pressure chamber (42) bounding on the sensingpiston, characterized in that a guide surface (60) for the sensingpiston (36) formed on the shaft (10) and a corresponding opposingsurface (64) formed on the sensing piston are each designed with aradial step (62, 66), so that a damping chamber (68) that contains fluidduring operation is formed between the guide surface and the opposingsurface, whose volume changes when the sensing piston is moved axiallyrelative to the shaft.
 2. Conical disk pair according to claim 1,characterized in that a fluid connection occurs between the dampingchamber (68) and the surroundings, exclusively between the guide surface(60) and the opposing surface (64).
 3. Conical disk pair according toclaim 2, characterized in that a sealing ring (70) is situated betweenthe sensing piston (36) and the shaft (10) on the side of the dampingchamber (68) that faces away from the outflow orifice (50).
 4. Conicaldisk pair according to one of claims 1 through 3, characterized in thatthe sensing piston is engaged with the input wheel (54) on its side thatfaces away from the movable disk (14).